The gear and adapter assembly in an automatic transmission gearbox is a crucial component responsible for transferring power from the engine to the wheels smoothly and efficiently. 

1. Gears: Gears are toothed wheels that mesh with each other to transmit power. In an automatic transmission, there are multiple gears of different sizes arranged in sets. These gears work together to provide different gear ratios, allowing the vehicle to accelerate, decelerate, and maintain speed efficiently.

2. Adapter Plate: The adapter plate serves as a mounting platform for the transmission assembly. It's typically made of durable materials like aluminum or steel and is designed to precisely align and attach the transmission to the engine block.